1. The Field of the Invention
The present invention relates to electrosurgical devices for ablating tissue in a surgical procedure. More specifically, the present invention relates to electrosurgical devices with an adhesive-free insulating piece surrounding the electrode.
2. The Relevant Technology
An arthroscope is an instrument used to look directly into a surgical site. Typically, the arthroscope utilizes a magnifying lens and coated glass fibers that beam an intense, cool light into the surgical site. A camera attached to the arthroscope allows the surgeon to view the surgical site on a monitor in the operating room. With the arthroscope, the surgeon can look directly into a surgical site, such as a knee or shoulder, to diagnose injury and decide on the best treatment. While viewing the surgical site with the arthroscope, the surgeon can repair an injury using a separate surgical instrument.
The ability to view the surgical site in this manner allows for a minimally invasive procedure. In recent years, arthroscopic surgeries have been developed for surgical procedures that traditionally were once very complicated and time consuming. Many of these surgeries are now performed as outpatient procedures using arthroscopic techniques.
At the beginning of the arthroscopic procedure, the patient receives an anesthetic. After the patient has been sufficiently anesthetized, the surgeon makes a plurality of incisions, known as portals, from the exterior of the body of the patient to the surgical site. Three portals are usually made: a first for the arthroscope, a second for the surgical instrument, and a third to permit fluids to escape from the surgical site. Sterile fluid is generally introduced by way of the arthroscope through the first portal. The sterile fluid serves among other purposes to expand the area of the surgical site. The insertion of sterile fluid makes it easier to see and work inside the body of the patient at the surgical site.
Electrosurgical instruments are a common device used in arthroscopy to ablate and/or coagulate tissue. In electrosurgery, an electrode is used to direct a high frequency current near or through body tissue. The high frequency current generates enough heat to ablate tissue. In monopolar electrosurgery the return electrode is a patch placed on the person. Energy that dissipates into the tissue connects the circuit by passing through the patch.
In a bipolar electrosurgical device, the return electrode is placed in a separate location on the electrosurgical device. Energy leaving the ablator electrode passes through fluids and/or tissue and returns to the return electrode on the electrosurgical device.
In both monopolar and bipolar electrosurgery, an electrode transfers energy to the surrounding fluid. The energy can be controlled to simply warm the adjacent tissue or to cut or ablate the tissue. Warming tissue is often done to facilitate coagulation. The heating event causes coagulation and thus can be used to stop bleeding in an arthroscopic procedure.
To ablate tissue, larger amounts of energy are applied to the electrode. The electrode generates enough heat to create gas bubbles around the electrode. The gas bubbles have a much higher resistance than tissue or saline, which causes the electrode voltage to increase. Given sufficient power the electrode discharges (i.e. arcs). The high voltage current travels through the gas bubbles and creates a plasma discharge over the surface of the electrode. Moving the electrode close to tissue causes the plasma discharge to come within a distance sufficiently close to ablate the tissue.
The contours and surface area of an electrode are important for controlling where arcing occurs on the electrode and how much power is required to cause a discharge. Current density is greatest at sharp edges. Arcing, and thus ablating, can be controlled by forming electrodes or electrode edges with small surface areas.
Typically, edges or small surface areas are created on an electrode by forming grooves or placing small wires. An important aspect of an electrode is that non-active surfaces must be electrically isolated from material such as the electrically conductive saline on the exterior of the electrode. Electrical conduction to these materials can ground the circuit and prevent the electrode from delivering its current to the active surface. For example wires or conducting materials that deliver current through the probe to the active surface need to be electronically isolated from the exterior of the probe, which can come into contact with body tissues during a procedure.
Much of the length of an electrosurgical probe is coated with an insulator or has lead wires that run inside insulated tubing. Near the active surface, however, insulating the electrodes becomes more difficult because of the extreme heat generated by the active surface. Many existing electrosurgical devices use an insulator such as a ceramic piece to protect the active portion of the electrode. For example electrodes that use multiple pins typically have a ceramic piece with holes for each of the pins. The pins are inserted through the holes and then the ceramic piece is glued to the probe's tubing using a temperature resistant adhesive.
Likewise, many single piece electrodes use a ceramic ring that encircles the active portion of the electrode. Typically the electrode is welded to an electrode seat or other tubing. The ceramic piece is then placed around the active portion of the electrode and glued using a temperature resistant adhesive.
Often, the ceramic piece only covers a small portion of the electrode near the active portion of the electrode. This practice is due to the fact that the extreme temperatures reached by the active surface dissipate very rapidly with distance away from the active surface. After a small distance other materials which are less resistant to temperature can be used as an insulator.
One problem with gluing the insulating piece to the probe using a temperature resistant adhesive is that the adhesive bonds can fail due to local high temperatures. Although the failure rates of the insulating piece are somewhat low, the consequences of the ceramic piece failing are very undesirable. If an insulating piece breaks off it falls into the operating cavity. Surgeons are often reluctant to leave foreign material in a person's body and thus spend precious time looking for the piece through the arthroscope. Furthermore, failure of the insulating piece is undesirable because it requires the surgeon to replace the instrument, thus increasing costs.
Another disadvantage of gluing the ceramic piece to the electrode is the expense incurred to manufacture the electrode. Electrosurgical probes are very small and asseyymbled by hand. Gluing a small insulating piece to the insulator using a temperature resistant adhesive is a labor intensive step that increases the complexity and expense of manufacturing the electrosurgical instrument.
Therefore, what is needed is an electrosurgical device that prevents the insulating piece from failing and simplifies the manufacturing process.